Common human cancers have been found to be frequently associated with mutations in dominant and recessive oncogenes, including the ras and p53 genes, and often produce mutant oncogene proteins that are uniquely present in the patients cancer but not in his/her normal cells. These tumor specific proteins could form the basis for highly tumor specific immunotherapy which targets an epitope that is present in each cancer cell and is fundamental to the maintenance of the malignant phenotype. In this project, we will characterize naturally occurring humoral and cellular immune responses to these mutant proteins, and analyze polymorphic or somatic changes in proteins involved in the processing and presentation of these antigens. The immune cells responsible for tumor cell killing appear to be major histocompatibility complex (MHC) class I restricted cytotoxic T lymphocytes (CTL). It is now known that such T cells detect target cells for killing by recognizing short peptide fragments of endogenous proteins which are presented to them by class I MHC molecules on the surface of the target cell. Such naturally presented peptides are found to be 8 or 9 residues long and are generated by endogenous antigen processing of both intracellular and membrane proteins. The peptide motif bound by several human class I molecules in known. We have developed an effective method of peptide vaccination in mice and have produced CTL specific for mutant human p53s expressed in murine cells. In this project, patients with breast cancer will have their tumors' oncogene mutations and HLA-A subtype determined and tumor specific mutant oncopeptides consistent sequences will be synthesized. We will use these peptides to stimulate mutant oncogene- specific CTL in vitro. In order to better understand escape from immune surveillance, we will also screen for polymorphic variation and somatic mutation in genes involved in antigen presentation such as the peptide transporters TAP1 and TAP2. We have evidence that frequent variation exists. In previous work in human lung cancer, we have demonstrated anti-tumor antibody responses, including those against mutant p53, and shown an association of anti-tumor antibody response with survival. In this project, we will extent these observations to human breast cancer. The ultimate goal is to understand the host immune response to mutant oncogene products, and to develop immunotherapies for human breast cancer patients based on specific oncoprotein mutant epitopes found in their tumors, and such a clinical trial is being developed.